A number of systems exist for applying labels to containers. A typical system may utilize either roll-fed labels or cut-and-stack labels. Other systems are also known, but may be viewed generally as variations on the two primary systems.
Prior art labeling apparatus and methods employing labels in roll-fed form may also include label cutting and registration means for severing discrete labels from the roll and then registering them for attachment to the containers through, for example, a vacuum transfer drive system. In these continuous application systems, an adhesive may be applied to the label, such as a hot-melt adhesive. The hot-melt adhesive is typically applied to both the leading and trailing edge of the backside of the labels, though it may also be applied to the entire backside, for attaching labels to containers. Roll-fed labeling systems may commonly be used to apply labels sequentially to containers, such as bottles, tubs, or jars, in a continuous label application system.
As one alternative, cut-and-stack labels, i.e., labels that have been pre-cut off-line and are retained or positioned in a stack within a dispenser, such as a label magazine, may also be applied sequentially to containers, such as bottles, tubs, or jars, in a continuous label application system. The cut-and-stack method may also employ a cold-glue adhesive, which may be water-soluble, though a hot-melt adhesive may also be used. When a cold-glue adhesive is employed in a cut-and-stack method, it may be applied to a label pallet by a roller application system including a spinning roller made of, for example, steel and/or having a surface made of rubber. A label pallet may be moved into contact with the first or exposed label of the stack to both apply the cold-glue to that label and remove the label from the stack through surface adhesion between the label and the relatively high viscosity and/or tacky adhesive. Thereafter, the label, with the cold-glue adhesive thereon, may be moved to a transfer drum, from which it may then be applied to a container, such as, for example, a bottle.
In one aspect of present labeling technology using high viscosity adhesives, the adhesive may be applied to the label by pumping the adhesive onto a spinning glue roller, the adhesive on the spinning roller is then wiped by a doctor blade to remove excess adhesive. A label pallet contacts the adhesive on the spinning glue roller, thus splitting the adhesive between the spinning glue roller and the label pallet. Cut-and-stack labeling systems typically use a relatively high viscosity adhesive, such as, for example, a cold glue adhesive. Roll-fed systems employing hot-melt adhesives also include relatively high viscosity adhesive. The viscosity of such high viscosity cold glue adhesives and hot-melt adhesives are often greater than about 30,000 to 50,000 centipoise.
Due to the viscosity of the adhesive, when the label pallet contacts the spinning glue roller to transfer the adhesive from the spinning glue roller to the label pallet, a pattern may commonly be generated on the surface of the label pallet due to varying concentrations of adhesive across the label pallet surface and resulting from the cohesive split of the adhesive between the label pallet and the spinning roller. This so-called “transfer splitting pattern” may be further passed to the label when the label is peeled from the label pallet. A typical transfer splitting pattern may include a series of non-uniform peaks and valleys, and may result in uneven glue adhesion between label and container and impaired appearance. Uneven adhesion between label and container may result in (i) poor label adhesion to the container, (ii) a non-uniform label appearance, and (iii) an easily identifiable interface between label and container. The transfer split pattern may be transferred to the label when the label is removed from the label pallet and then transferred to the container.
Under an opaque label, the pattern or other visual imperfections may not be of significant concern, unless the appearance is manifest through the container wall, such as with clear containers, or if it appears on the surface of the label. However, under a transparent or clear label, the split-transfer adhesive pattern may notoriously appear through the label or otherwise impair the appearance of the labeled container. This problem may be particularly noticeable when trying to achieve a no-label look.
To address this problem, labeling technology has turned to two-part cold glue adhesives in which the labels comprise an activatable adhesive coating or layer on a surface of the label. The components of the activatable adhesive may constitute the high viscosity components of a traditional adhesive system, such as a cold glue system. These components are incorporated onto a surface, often a backside surface, of a label. Such components are dried, when necessary, and form an activatable adhesive coating or layer. Thereafter, a low viscosity activator solution is applied to the activatable adhesive label to activate the adhesive. The activated adhesive on the label is applied to a container while the adhesive is still tacky to the touch.
These low viscosity activator solutions may preferably constitute a solution that is relatively lower in viscosity as compared to an adhesive compound, such that the low viscosity activator solution may relatively easily be applied to the activatable adhesive on a surface of the film by spraying, to activate the adhesive. When such activated labels are applied to containers the appearance of the adhesive pattern on a labeled container is reduced.
These low viscosity activator solutions have a viscosity in the range from 5 to 1000; preferably from 5 to 500; more preferably from 5 to 100 centipoise.
Current labeling lines that use high viscosity adhesives are not capable of utilizing the low viscosity activator solutions. The need exists to retrofit the label application stations used for high viscosity adhesives in order to incorporate such lower viscosity activator solution. Such retrofit should be low in cost, easy to implement, and should require minimal to no change to existing labeling equipment. The present invention meets these and other needs.